1. Field of the Invention
The invention relates to a multi-axis mechanical manipulator with adjustable travel and with complete protection against overloads.
2. Description of the Prior Art
A wide variety of bi- or triaxial mechanical manipulators already exists, differing principally in the indexing mechanism used: global cam, paired flat cams, and cylindrical cams. This last means is reserved principally for triaxial mechanical manipulators.
Nevertheless, despite the undeniable advantages of compact construction, high precision, high transfer speed, controlled acceleration, positive positioning, reduction of idle time, and so forth that these indexing mechanisms offer, they have the disadvantages associated with rigidity, which are:
the movements are sluggish; the linear and angular displacements are fixed and are not adjustable; PA1 the laws of motion are selected to obtain optimal acceleration and deceleration conditions, which yield a maximum speed at mid-course; PA1 the stops at mid-course translate into pronounced shocks, because in the majority of cases the indexing mechanisms are driven by a sliding rotor motor and a worm wheel reducing gear. PA1 after triggering, the initial position of the manipulator platform or arm must be searched for; this requires precise knowledge of the material and often as a result means a stoppage in production, resulting in losses in productivity; PA1 upon triggering, the masses in motion are no longer controlled and thus become dangerous, especially for vertical movements; PA1 the triggered torque limiter must be monitored electrically; PA1 furthermore, the triggered torque limiter lessens precision, which consequently precludes its being used for high-precision indexing or positioning applications.
Moreover, if the output shaft becomes stuck in the locked position, there is a risk that the rollers or cam will break, because they are located in the zone of stoppage of the cam.
The angle of cam/roller pressure is equal to zero, so that in the presence of even slight torque exerted on the camshaft the forces on the rollers tend to infinity.
To prevent the risk of breakage, torque limiters that are triggered in the case of blockage are typically used, but they entail the following disadvantages:
An overload protector for mechanical manipulators is already known such as that described in French Patent Application FR A 2.451.250, which relates to materials handling apparatus including two cylindrical cams, the second of which is associated with a roller mounted in such a way that it can oscillate about an axis transverse to that of the cam, so that in combination with a means for disengagement in the case of overload, such as a spring engaging and disengaging means, it can permit a movement of the cam in question without being accompanied by a movement of the grasping means when the latter encounters an obstacle. Nevertheless, the disengagement means used (the spring engaging and disengaging means functioning as a torque limiter) necessitates searching for the initial position of the manipulator arm after use, with the attendant interruption in production.